1. Field of the Invention
This invention generally relates to housings and methods of assembling automotive ignition distributor system components. More particularly, this invention relates to a housing and a method of housing a magnetic circuit and a circuit board for an automotive ignition distributor system having a Hall effect sensor.
2. Description of the Prior Art
Hall effect devices provide an output voltage proportional to the magnetic flux passing therethrough. In order to maximize the output voltage of such a device, it is desirable, therefore, to maintain the flux density through such a device as great as possible. This may be accomplished by keeping the reluctance of the magnetic circuit providing the magnetic flux for the Hall device as small as possible. Since the reluctance of a magnetic circuit is directly proportional to the length of an air gap in the magnetic circuit, it is desirable to control the air gap length as precisely as possible.
Hall effect sensors used in automotive ignition distributor systems provide timing signals for said automotive systems. A distributor shaft coupled to the engine has attached thereto a rotor member having a plurality of peripheral vane members extending therefrom. The vanes may be made of a high permeability ferrous material and alternately pass through an air gap in the magnetic circuit containing a Hall device positioned within the air gap. The flux which passes through the Hall device is shunted away from the Hall device by the vanes. Since it is desirable to maintain the reluctance of the air gap as small as possible, it is desirable that the dimensional variations of the air gap be as small as possible, requiring either precision alignment of or tight tolerances for all the components forming a Hall effect sensor circuit.
Some prior art Hall effect sensor assemblies for use in automotive ignition distributor systems, are contained in molded plastic holders. An air gap is provided for the passage of the vane through the holder and on each side of the air gap are molded portions for containing a magnetic and pole piece assembly and a circuit board assembly containing a Hall effect device and a flux concentrator. Appropriate recesses and slots are molded in the prior art holders for containing the aforementioned components. Since a molded holder has dimensions which will vary within certain tolerance limits, the relative positions of the circuit board, the concentrator, and the magnet and pole piece assembly with respect to each other are subject to variations. It is ultimately desired that the vanes moving through the air gap in the magnetic circuits pass through a gap which is as small as possible. However, it is not possible to provide an air gap of minimum dimensions due to expected tolerance variations of the various component parts and of holder dimensions. The air gap, therefore, sometimes must be made wider than necessary to allow for passage of the vanes.
In addition to the requirement for having an air gap wider than necessary because of dimensional variations in the holder dimensions and the components of a Hall effect sensor assembly, dimensional tolerances between the circuit board containing the Hall effect sensor and the flux concentrator also are present. The dimensional variations in the location of the Hall effect sensor holder with respect to the distributor shaft axis must also be accounted for.
The method for assembling prior art components in a housing involves placing the components within predetermined molded recesses within the housing and fixing said components in place, which because of variation in the housing and component tolerances does not provide a precisely controlled air gap.
Since the circuit board is contained within the housing, which is generally formed from a non-conductive material, heat producing circuit components may not be utilized in such assemblies. For example, integral zener diode regulator circuits, which are particularly useful in automotive applications, are not easily housed in a molded plastic housing assembly.